In seismic surveying, seismic data may be acquired by imparting acoustic energy into the Earth near its surface, and detecting acoustic energy that is reflected from boundaries between different layers of a subterranean formation. Acoustic energy is reflected when there is a difference in acoustic impedance between adjacent layers to a boundary. Signals representing the detected acoustic energy are interpreted often with seismic imaging to infer structures and composition of the subterranean formation, thereby to aid in the identification and production of hydrocarbons.
In marine seismic surveying, a seismic energy source, such as an air gun, or air gun array, marine vibrator, or marine vibrator array, is typically used to impart the acoustic energy into the subterranean formations below the bottom of a body of water. The seismic energy source is actuated at a selected depth in the water, typically while the seismic energy source is being towed by a vessel. The same or a different vessel tows one or more seismic sensor cables, called streamers, in the water. Generally the streamers extend behind the vessel along the direction in which the streamer is towed. Typically, a streamer includes a plurality of sensors, such as hydrophones, for example, disposed on the cable at spaced apart, known positions along the cable. Hydrophones are sensors that generate an optical or electrical signal corresponding to the pressure of the water or the time gradient of pressure in the water. The vessel that tows the one or more streamers typically includes recording equipment to make a record, indexed with respect to time, of the signals generated by the sensors in response to the detected acoustic energy. The record of signals may be processed and analyzed with seismic imaging to infer structures of and compositions of the subterranean formations below the locations at which the seismic survey is performed.